SUN, MOON, AND TIDES — COLBERT 



187 



mation, in recent years, on the behavior of the tide at various seaports 

 and along the open coast. 



When a tide gage is operated through a full month, there is traced 

 on a continuous roll of paper a line showing the rise and fall of the 

 tide for that period. Observations are usually continued month after 

 month, and, at basic stations, year after year. From the curve traced 

 on the tide-gage record, there can be obtained the times of high and 

 low water, the heights, the range of tide, and the height of water at 

 any intermediate time between high and low water. Studies of the 

 tide curves at various ports have disclosed differences in time, range, 

 and characteristics. We have learned of varieties in the tides which 

 occur because different water areas react to the same tide-producing 

 forces in different ways. 



Figure 1. — Tide curves, New York, Pensacola, San Francisco. 



Let us look at the tide curves of some of our coastal seaports and 

 note the differences exhibited. Figure 1 shows the actual curves, 

 recorded on automatic tide gages, of the rise and fall of the tide on the 

 same day at New York, Pensacola, and San Francisco — that is, for a 

 seaport along the Atlantic, the Gulf, and the Pacific coasts. At each 

 port, the central horizontal line represents the mean level of the sea, 

 above and below which the water has risen or fallen in the amounts 

 shown in feet to the left. At New York there are two high and two 

 low waters in a period of a day; the morning and evening tides do 

 not differ much and the tide has risen above the mean level of the 



